This invention relates generally to fluid heaters and more particularly to fluid heaters specifically designed for the utilization of bulky solid fuels.
Bulk fuels such as wood have had a resurgence in popularity as the cost of oil and gas have surged in recent years. However, while effective wood burners and boilers have been available for many decades, the increased cost of energy has only recently renewed interest in applying new materials and design techniques to the age-old tasks of burning wood and heating water.
Boilers have been proposed that circulate water through or around a firebox to allow it to extract heat from the combustion process. Recently proposed designs have sought to utilize the circulating pipes themselves as functional elements in the combustion chamber. Carlson U.S. Pat. No. 3,934,554, for example, discloses a water heater in which water chambers or tanks on either side of the firebox are interconnected by upper and lower conduits, the lower conduits being spaced to function as grates to hold the fuel. A substantial amount of manufacturing expertise and labor is required to interconnect the upper and lower conduits to the water jackets of the Carlson unit, thus providing a substantial economic drawback to the utilization of such a unit.
Substantial advances have also been made in the design of wood stoves with an eye toward substantially improving their efficiency. It has been observed that high levels of efficiency require a stove design that is essentially air-tight to provide for complete combustion. Most high-efficiency units utilize controlled air intakes to provide just enough oxygen to burn the wood as completely as possible without releasing unburned gases up the chimney. Internal baffles and vents have been incorporated in numerous wood stoves to aid in the combustion process by introducing secondary air to the gases released from the primary combustion process and burning this air-enriched mixture completely within the combustion chamber. Two step stoves of this type are very efficient and reduce the amount of leftover ash to a minimum.